This invention relates to an inhalation device by means of which metered doses of medicament in the form of a powder can be dispersed to a user. In particular it relates to a device of the type in which the medicament powder is held in bulk in a reservoir with which the device is provided, and is metered to the user from the reservoir.
In devices of the type just described, it is difficult to obtain doses which are equal to a nominal value to within the appropriate tolerance. It will be understood that the tolerance permitted is often very small, as it is important that the user should be given a dose which is very close to the nominal value. In order to maintain the medicament powder in a manageable state it needs to be kept dry. Any ingress of moisture into the reservoir from outside can cause the medicament powder to agglomerate and this may be detrimental to its free flowing properties rendering it difficult to meter consistent doses from the reservoir. In the absence of adequate reservoir sealing it may be necessary to incorporate a desiccant cartridge into the reservoir to absorb any moisture that does enter. This is often insufficient to prevent deterioration of the medicament powder.
It is an object of the present invention to provide a device of the type just described, in which doses can be repeatedly accurately dispersed, without requiring a dispensing mechanism of undue complexity.
It is a further object of the present invention to provide a device of the type just described, but which additionally incorporates a simple and efficient sealing means to prevent ingress of moisture into the reservoir.
According to the present invention there is provided an inhalation device comprising a body defining a reservoir for medicament in the form of a powder, an outlet through which a user can inhale, and a dosing member with at least one metering recess formed therein, the dosing member being moveable between a first position in which the at least one metering recess communicates with the reservoir to receive a dose of powder therefrom and a second position in which the at least one metering recess communicates with the outlet to permit the user to inhale the dose, the at least one metering recess being formed in a face of the dosing member, the said face being mounted in contact against a similar mating face of the body at the lower end of the reservoir, and at least one moveable weight adapted, when the device is shaken, to strike an anvil surface defined in the device.
The at least one weight may be slidable longitudinally of the device in a respective bore, with the anvil surface being at the lower end of the bore.
Alternatively the weight may be in the form of a ring encircling the device and slidable longitudinally thereof.
According to a further aspect of the invention the face of the dosing member and the mating face of the body are sealing faces with highly polished smooth surfaces which form a sliding seal which excludes substantially all air from the interface therebetween.
Suitably the sealing faces have a surface texture sufficiently smooth to have a roughness average value (Ra) of 0.5 microns or less, preferably 0.2 microns or less.
Suitably the sealing faces are flat. More suitably they have a flatness of 0.005 mm or less, preferably 0.003 mm or less.
Alternatively the sealing faces may be frusto-conical. The sealing faces may alternatively be cylindrical. In a further alternative the sealing faces may be spherical.
The sealing surfaces are suitably made of a hard rigid material such as acetal resins, ceramics or metals.
A further aspect of the invention provides an inhalation device comprising a reservoir for medicament in the form of a powder, an outlet through which a user can inhale, a metering means adapted to communicate with the reservoir to receive a dose of powder therefrom and with the outlet to permit the user to inhale the dose, and at least one weight moveable in the device and adapted, when the device is shaken, to strike an anvil surface defined in the device.
Additionally the invention provides an inhalation device comprising a body forming a reservoir for medicaments in the form of a powder, an outlet through which a user can inhale, and a dosing member with at least one metering recess formed therein, the dosing member being moveable between a position in which the at least one metering recess communicates with the reservoir to receive a dose of powder therefrom and a position in which the at least one metering recess communicates with the outlet to permit the user to inhale the dose, the at least one metering recess being formed in a face of the dosing member, the said face being mounted in contact against a similar mating face of the body, characterised in that the said face of the dosing member and the said mating face of the body have highly polished smooth surfaces which form a contacting face to face kinetic seal which excludes substantially all air from the interface. The term xe2x80x98kinetic sealxe2x80x99 in this context means a seal that can withstand relative movement of the two faces.
Another embodiment of the invention provides an inhalation device comprising a body defining a reservoir for medicament in the form of a powder, an outlet through which a user can inhale, and a dosing member with at least one metering recess formed therein, the dosing member being moveable between a first position in which the at least one metering recess communicates with the reservoir to receive a dose of powder therefrom and a second position in which the at least one metering recess communicates with the outlet to permit the user to inhale the dose, the at least one metering recess being formed in a face of the dosing member, the said face being mounted in contact against a similar mating face of the body at the lower end of the reservoir, characterised in that the said face of the dosing member and the said mating face of the body are sealing faces with highly polished surfaces which form a sliding seal which excludes substantially all air from the interface therebetween.